1. Field of the Invention
The present invention pertains to apparatus for gaining access to the interior of containers. More particularly, the present invention is related to holders for mounting equipment such as sensing or measuring devices within high pressure containers, and tools for inserting and retrieving such holders without exposing the interior of the container to the surrounding atmosphere. Such apparatus is particularly applicable to high pressure fluid pipelines whereby sensors, such as corrosion or scale testing coupons, may be inserted into the fluid flow and retrieved therefrom without shutting down the pipeline flow.
2. Description of Prior Art
In various industrial settings, it is often necessary to test or sample material under pressure in a pipeline or other enclosure. Access to such material may conceivably be had by first relieving the pressure, or shutting down the flow in the pipeline. This may be a difficult or dangerous procedure, and will usually be expensive. Retrieval tools, or retractors, are known for inserting holders or other fittings through a hole, for example, in the side of a pipe member without the need for shutting down the high pressure pipeline flow. The retrieval tools are also used to withdraw the holders from the pipeline without losing pipeline pressure.
While the holder is in position extending into the interior of the pipeline, a seal is maintained between a fitting mounted on the pipeline and the holder, or equipment attached thereto. During the removal of the holder from the pipeline, continuous sealing to maintain the pipeline pressure must be carried out. The holder must be capable of being totally withdrawn from the pipeline to allow access to testing equipment mounted on the holder for insertion within the pipeline. Thus, the fitting secured to the pipeline must be provided with a valve or other closure device to seal off the pipeline in the absence of the holder.
According to some prior art practices, a valve such as a gate valve is permanently installed on a fitting attached to the pipeline to selectively open and close communication to the tap hole in the side of the pipe. To install a holder extending into the pipeline a retrieval tool is secured and sealed to the valve housing with the holder positioned within the retrieval tool. The valve is opened and the retrieval tool is operated to advance the holder through the valve passage toward the pipeline. The procedure is generally reversed to retrieve the holder from the pipeline.
One type of retrieval tool must remain sealed to the valve housing as long as the holder is in position extending into the pipeline. In such case, the integrity of the sealing of the pipeline pressure is maintained by seal members carried by the retrieval tool rather than the holder.
In another type of tool, the holder may be sealed to fittings attached to the pipeline, and the retrieval tool removed. However, movement of the holder toward or away from the pipeline in the latter case is effected by moving a rod, to which the holder is attached, through a packing gland. A pressure differential across the packing gland may result in unintended movement of the rod.
Advancement of the holder according to prior art apparatus is generally achieved by rotating a screw device to which the holder is attached. Such rotation precludes the use of a metal-to-metal seal between the holder and the pipeline fittings. Another disadvantage of such rotation of the holder is the difficulty in providing the exact alignment within the pipeline of the equipment mounted on the holder. For example, where material testing samples, or coupons, are being placed within a high pressure fluid flow, the effect on the testing material may be altered depending on the orientation of the coupon relative to the direction of fluid flow. Generally, where scaling effects are to be determined, the coupon which is laminar in shape is placed with a flat side perpendicular to the direction of flow. For corrosion testing, coupons are placed parallel to the flow direction. Where the holder is advanced solely by a screw action, the orientation of attached coupons will be determined by the final position of the holder relative to the pipeline fittings. Even where additional orientation adjustments to the holder and attached coupons may be made, such adjustment may be difficult and dangerous operations due to the high pressure within the pipeline. Furthermore, since the operator cannot see the coupon, he must depend on fiducial marks on the holder if exposed, or on the retrieval tool.
Another type combination retrieval tool and holder is known whereby the holder may be secured and sealed to a fitting on the pipeline without the need for a permanent valve installation. To insert or to remove the holder a valve is connected to the pipeline fitting, and the retrieval tool is sealed to the top of the valve housing. The valve is opened and the retrieval tool is operated to advance a rod through the valve passage to either insert or retrieve the holder. Again, advancement of the holder is effected by rotating the rod to which the holder is attached. Thus, as discussed hereinbefore, a metal-to-metal seal between the holder and the pipeline fitting is precluded. Also, the holder and attached coupons must be oriented after the holder is sealed to the pipeline fitting. In this particular type of tool, rotation of the rod to advance or retract the holder is effected by turning an exterior sleeve of the tool.
Gaining access to the interior of a high pressure pipeline may be dangerous, particularly where such procedure is carried out manually. Consequently, it is highly desirable that retrieval tools and holders be designed to maximize safety and ease of use. For example, in the case of a blowout during operations with the retrieval tool, it may be expected that the major thrust of the escaping pressurized fluid will be along the pipeline fitting perpendicular to the pipeline itself. Thus, it is preferred that the retrieval tool be operable without the need for the operator to be positioned above the retrieval tool, in line with the possible blowout thrust. Further, the tool should be light weight and require no awkward or difficult movements by the operator in, for example, effecting rotation of an internal mandrel. It is also advantageous if the tool is designed for operation by one operator so that the coordination of movements by two or more individuals is unnecessary. Finally, the uncertainty of the orientation of the equipment positioned within the pipeline may be removed by a holder which is automatically oriented as desired when finally positioned on the pipeline.